C. Hartnig et Mtm. Koper, Molecular dynamics simulations of solvent reorganization in electron-transfer reactions, J CHEM PHYS, 115(18), 2001, pp. 8540-8546
We present molecular dynamics simulations of solvent reorganization in elec
tron-transfer reactions in water. Studying a series of solutes with the sam
e core radius (typical for chlorine) but with varying charge from -3 to +3,
the simulations show that the single-solute solvent reorganization energy
depends quite strongly on the solute's charge, in contrast with the continu
um Marcus theory. Due to the ion-dipole interactions, electrostriction play
s an important role for charged species. The effective radius of a neutral
species is comparatively larger, making the solvent reorganization energy s
mall. Strong increases in the solvent reorganization energy occur when the
solute is charged to either -1 to +1, due to the significantly smaller effe
ctive radius caused by the ion-dipole interactions. However, the effect is
nonsymmetric because the center of the water dipole can approach closer to
the negative species than to the positive species. Hence, the nonlinearity
occurs mainly in the transition from 0 to -1. For higher charges (+3, +2, -
2, -3), dielectric saturation causes a decrease in the reorganization energ
y with increasing charge. We also calculate the equilibrium activation ener
gy for an outer-sphere electrochemical electron-transfer reaction of the Xe(-)reversible arrowX(-) type, with varying of the core radius of the X spe
cies. The deviations from Marcus theory are relatively small for large reac
tants, but get more significant for small reactants. This is mainly due to
the fact that the changes in electrostriction have a comparatively large ef
fect for small solutes. (C) 2001 American Institute of Physics.